Glycosphingolipids in mammalian cells appear to be localized almost exclusively in the external surface of the plasma membrane. These lipids have been known for some years to act as antigenic determinants and mediators of immune responses. Recent work suggests that specific glycosphingolipids may serve as receptors for toxins, viruses and some peptide hormones. There is also a growing body of evidence associating alterations in cell glycosphingolipids with normal process such as growth, differentiation, development and aging and also with oncogenic transformation in many cell types. In addition glycosphingolipids seem to be involved in cell-cell interactions and recognition. Although there is considerable information about the molecular structure of many glycosphingolipids, relatively little is known about the organizations of molecules of this class in phospholipid bilayers and the bilayers of biological membranes. It seems certain that their molecular organization is a critical parameter underlying many of the functions of glycosphingolipids. The research supported by this grant centers on the investigation of the biologically relevant system properties of lipid bilayers from well characterized phospholipids and cholesterol which contain variable amounts of glycosphingolipids of the types found in mammalian cell plasma membranes. Emphasis will be placed on the examination of bilayers in the form of single lamellar vesicles which have glycosphingolipid incorporated only on the outer surface; a system which is the analog of the plasma membrane bilayer. Multilamellar liposomes as well as large and small unilamellar vesicles will be utilized in this work which will depend upon a variety of physical techniques including fluorescent probes and NMr spectroscopy (1H, 2H, 13C and 31P), scanning calorimetry, partial molal volume measurement, autocorrelation light scattering as well as hydrodynamic methods to characterize vesicle dispersions. These studies complement a freeze-etch electron microscopic investigation carried out on similar systems as well as on selected biological membranes as a collaborative effort with Dr. Thomas Tillack in the Department of Pathology.